182 STREBLOSOMA BAIRDI. 



1915. Streblosoma cochleatum, Caullery. Bull. Soc. Zool. France, t. xi, 1 — 3, p. 52. 

 1917 - „ Bairdi, Hessle. Zool. Bidr. Uppsala, Bd. v, p. 211. 



Habitat.— Dredged in 80 — 90 fathoms in Busta Voe, St. Magnus Bay, by Dr. Gwyn 

 Jeffreys in 1867 and 1868. Dredged at Station No. 6 (Atlantic) in the " Porcupine " 

 Expedition of 1870. Elsewhere it occurs in Sweden (Malmgren, Malm). 



The cephalic lobe is truncate in lateral view — a feature due to the flattened arch of 

 the supra-oral fold, which in many Terebellids forms a spout- or hood-like projection. 

 The surface of the cephalic plate from which the tentacles arise is thus nearly vertical. 

 The dorsal collar presents no eye-specks in the preparations, and curves downward to 

 join the supra-oral fold externally and ventrally. The tentacles agree with those of 

 Thelepus, being well developed and having a deep groove with frilled margins. 



The general outline of the body agrees with that in Thelepus, though the details 

 differ. It is enlarged anteriorly and tapered posteriorly, no example, however, being 

 complete. The dorsal surface is rounded and smoother than in Thelepus, the ventral 

 surface flattened, and posteriorly slightly grooved. Anteriorly are ten to eleven glandular 

 ventral shields, which may be wrinkled in the preparations, and the outer edges of which 

 touch the rows of hooks. A glandular belt accompanies the setigerous region, but it is 

 not so pronounced dorsally as to form anteriorly the definite edge as in Thelepus, though 

 posteriorly it is well defined. The ventral surface behind the shields is more thinly 

 coated with the glandular tissue, and a thickened median ridge continues for some 

 distance backward. The Norwegian examples appear to be smaller than the British. 



Though Thelepus t/riserialis agrees with Streblosoma bairdi in having three pairs of 

 branchiaa, yet their arrangement in connection with the bristle-tufts differs. In the 

 present form a branchial tuft of several filaments occurs on the anterior edge of the 

 second segment, but its attachment is above the line of the first setigerous process, which 

 is likewise on the second segment. Behind is a second tuft of branchia3 with fewer 

 filaments, and which is in a line with the first setigerous process of the left side ; whilst 

 on the right it is opposite the second setigerous process. The third is a prominent group 

 of about six filaments opposite the third bristle-tuft. The individual filaments are 

 similar to those of Thelepus, though in some they are longer; and the first set arise from 

 a transverse ridge, which, however, does not pass externally below the line of the bristles 

 as in Thelepus. On the whole the area covered by the branchige is longer antero- 

 posteriorly than in Thelepus. 



No more distinctive feature between Streblosoma and Thelepus exists than 

 the great size of the setigerous processes and the length of the bristles. The first 

 setigerous process occurs on the second segment, and it is slightly shorter than those 

 which follow, and in the region of the shields the processes form long lamellse with 

 slightly expanded tips set obliquely like the blades of a series of oars, the ventral edges 

 of which are curved and split for the extended line of pale golden bristles. Moreover, 

 when the process is removed a distinct twist like the blade of a propeller occurs in all 

 the pencils of bristles — a condition closely connected with the functions of the bristle- 

 tufts. As in Thelepus the setigerous processes spring from the posterior part of each 

 segment and are dorso-lateral in position. Two ranges of bristles occur in each tuft, 



